The present invention relates to a wrench, and more specifically to a box end for a box end wrench which has a substantially .OMEGA.-shaped constraint spring rod mounted in the box end for stopping the workpiece in the box end, enabling the workpiece to be positively turned with the box end wrench.
A variety of box end wrenches have been disclosed, and have appeared on the market. FIGS. 1 and 2 show a regular box end wrench. This structure of box end wrench has a handle, and a box end at one end of the handle. The box end defines a box for attaching to the hexagon head bolt or hexagon nut to be turned. When the box end wrench is attached to for example a hexagon head bolt, the box end may slip from the hexagon head of the hexagon head bolt when box end wrench is turned with the hand. FIGS. 3 and 5 show another structure of box end wrench according to the prior art which comprises a steel ball mounted in a hole on a flange at one side of the handle and suspending above the box at the border area. When the box end of the box end wrench is attached to the hexagon head bolt to be turned, the steel ball is stopped at the top of the hexagon head of the hexagon head bolt, enabling the hexagon head bolt to be positively turned with the box end wrench. This structure of box end wrench is not durable in use because the steel ball wears quickly with use. Further, the steel ball can not positively stop the wokpiece in place and an excessive downward pressure is given to the box end. FIGS. 4 and 6 show still another structure of box end wrench according to the prior art which uses a sliding bar for securing the box end to the workpiece. This structure of box end wrench is inconvenient in use because the sliding stop bar must be frequently moved in and out along the handle. Further, the application range of the box end wrench is limited. FIGS. 7 and 8 show still another structure of box end wrench in which an inward annular flange is provided at one side of the box in each box end. Because the inward annular flange is integral with the inside wall of the box end, it is difficult to process teeth on the inside wall of the box end.
It is one object of the present invention to provide a box end for a box end wrench which firmly secures the workpiece in place, enabling the workpiece to be positively turned with the box end wrench. It is another object of the present invention to provide a box end for a box end wrench which is easy to manufacture. It is still another object of the present invention to provide a box end for a box end wrench which is practical for a mass production to reduce the manufacturing cost. According to the present invention, a substantially .OMEGA.-shaped constraint spring rod is mounted inside the box end of the box end wrench for stopping the workpiece in the box end, enabling the workpiece to be positively turned with the box end wrench. The constraint spring rod has two opposite ends respectively inserted into two opposite radial through holes on the peripheral wall of the box end, and an arched middle section closely attached to the inside wall of the box end for stopping the workpiece in the box end.